Fast automatic gain control for high performance wireless communications in substation automation

1. A method for automatic gain control in a wireless communication network employing time based scheduling of packets, the method being performed by a packet receiver in the wireless communication network, the method comprising:

receiving a packet from a packet transmitter, the packet comprising a preamble, and the preamble being composed of a single orthogonal frequency-division multiplexing (ODFM) symbol and represented by a sequence of samples;

applying automatic gain control to the sequence of samples after variable gain amplitude control has been applied to the sequence of samples, the automatic gain control involving applying a low-pass filter (LPF) to the sequence of automatic gain controlled samples, the LPF being selected from a bank of LPFs which LPF to apply depends on, according to the time based scheduling, from which packet transmitter the packet is received, and applying the automatic gain control producing an automatic gain control value, the automatic gain control value depending, via the LPF when not in a default state, on a previous automatic gain control value for the same packet transmitter; and

feeding the automatic gain control value as a control signal to be used during the variable gain amplitude control as applied to a next packet from the same packet transmitter.

2. The method according to claim 1 , further comprising:

applying the variable gain amplitude control to the sequence of samples, resulting in a sequence of variable gain amplitude controlled samples, and

the automatic gain control being applied to the sequence of variable gain amplitude controlled samples.

3. The method according to claim 1 , further comprising:

receiving an indication of relative movement between the packet receiver and the packet transmitter; and

in response to receiving the indication, resetting the LPF to the default state, wherein in the default state the automatic gain control value does not depend on any previous automatic gain control value.

4. The method according to claim 2 , further comprising applying a comparator to the sequence of variable gain amplitude controlled samples before applying the LPF.

5. The method according to claim 4 , wherein applying the comparator comprises comparing the sequence of variable gain amplitude controlled samples to a target gain value, and whcrcin the LPF is applied to a difference resulting from the comparing.

6. The method according to claim 4 , wherein one common comparator is applied irrespectively of from which packet transmitter the packet is received.

7. The method according to claim 4 , wherein the comparator is selected from a bank of comparators.

8. The method according to claim 7 , wherein which comparator to apply depends on, according to the time based scheduling, from which packet transmitter the packet is received.

9. The method according to claim 7 , wherein which comparators to apply depends on from which type of packet transmitter the packet is received.

10. The method according to claim 1 , wherein the packet receiver is part of a gateway, circuit breaker, circuit protector, transformer, or switchgear.

11. The method according to claim 1 , wherein the packet transmitter is part of a gateway, circuit breaker, circuit protector, transformer, or switchgear.

12. A packet receiver for automatic gain control in a wireless communication network for power grid control, the wireless communication network employing time based scheduling of packets, the packet receiver comprising processing circuitry configured to cause the packet receiver to:

receive a packet from a packet transmitter, wherein the packet comprises a preamble, wherein the preamble is composed of a single orthogonal frequency-division multiplexing (OFDM) symbol and represented by a sequence of samples;

apply automatic gain control to the sequence of samples after variable gain amplitude control has been applied to the sequence of samples, wherein the automatic gain control involves applying a low-pass filter (LPF) to the sequence of automatic gain controlled samples, wherein the LPF is selected from a bank of LPFs, wherein which LPF to apply depends on, according to the time based scheduling, from which packet transmitter the packet is received, and wherein applying the automatic gain control produces an automatic gain control value, the automatic gain control value depending, via the LPF when not in a default state, on a previous automatic gain control value for the same packet transmitter; and

feed the automatic gain control value as a control signal to be used during the variable gain amplitude control when applied to a next packet from the same packet transmitter.

13. The packet receiver according to claim 12 , wherein the processing circuitry is configured to cause the packet receiver to:

receive an indication of relative movement between the packet receiver and the packet transmitter; and

in response to receiving the indication, reset the LPF to the default state, wherein in the default state the automatic gain control value does not depend on any previous automatic gain control value.

14. The packet receiver according to claim 12 , wherein the processing circuitry is configured to cause the packet receiver to:

apply the variable gain amplitude control to the sequence of samples, resulting in a sequence of variable gain amplitude controlled samples, and

wherein the automatic gain control is applied to the sequence of variable gain amplitude controlled samples.

15. The packet receiver according to claim 14 , wherein the processing circuitry is configured to cause the packet receiver to apply a comparator to the sequence of variable gain amplitude controlled samples before applying the LPF.

16. The packet receiver according to claim 15 , wherein the processing circuitry configured to cause the packet receiver to apply the comparator comprises:

the processing circuitry configured to cause the packet receiver to compare the sequence of variable gain amplitude controlled samples to a target gain value; and

wherein the LPF is applied to a difference resulting from the comparison.

17. The packet receiver according to claim 15 , wherein the processing circuitry is configured to cause the packet receiver to apply one common comparator irrespectively of from which packet transmitter the packet is received.

18. The packet receiver according to claim 15 , wherein the processing circuitry is configured to cause the packet receiver to select the comparator from a bank of comparators.

19. The packet receiver according to claim 12 , wherein the packet receiver is part of a gateway, circuit breaker, circuit protector, transformer, or switchgear.

20. A non-transitory computer readable medium storing a computer program for automatic gain control in a wireless communication network for power grid control, the wireless communication network employing time based scheduling of packets, the computer program comprising computer code which, when run on processing circuitry of a packet receiver, causes the packet receiver to:

receive a packet from a packet transmitter, wherein the packet comprises a preamble, wherein the preamble is composed of a single orthogonal frequency-division multiplexing (OFDM) symbol and represented by a sequence of samples;

apply automatic gain control to the sequence of samples after variable gain amplitude control has been applied to the sequence of samples, wherein the automatic gain control comprises applying a low-pass filter (LPF) to the sequence of automatic gain controlled samples, wherein the LPF is selected from a bank of LPFs, wherein which LPF to apply depends on, according to the time based scheduling, from which packet transmitter the packet is received, and wherein applying the automatic gain control produces an automatic gain control value, the automatic gain control value depending, via the LPF when not in a default state, on a previous automatic gain control value for the same packet transmitter; and

feed the automatic gain control value as a control signal to be used during the variable gain amplitude control when applied to a next packet from the same packet transmitter.